From the point of view of functionality, one of the features Update Manger offers is orchestrated ESXi host updates. Since I got a few questions related to host updates, I will describe in the post how to do the update. In my case I updated from vSphere 6.5 to 6.5a. Not a big step, but enough to prove a point.
I've started by downloading the latest ESXi ISO from VMware site, then logged in vCenter Web Client and uploade the image in Update Manager. In Web Client go to Home - Update Manager - Manage tab - ESXi Images and select Import ESXi Image. Browse to the location of the ISO image and upload it.
After the upload is successful, the image will be displayed in the list imported images. Select it and you can see the software packages that are included in the image:
Now the desired image is in the repository. To use the image, we need to attach it to a baseline. Then the baseline will be attached to the hosts or clusters that we want to update. Right click on the image and select create baseline, type the name of the baseline, optionally add a description and press OK.
The baseline is displayed in Hosts Baseline tab:
After the scan finishes, the Non-Compliant message is displayed and we can start the remediation process. Pressing Remediate starts the wizard. First, select the baseline to apply (there might be other baselines attached to the hosts).
Then select the targets, in my case I've selected all the hosts in the cluster:
Accept the EULA, go to Adanced options and schedule the remediation to take place during a specific maintenance window or whether to ignore warnings that may appear during update. In this case we'll run the remediation immediately:
On Host remediation options select what to do with the VMs when hosts are put into maintenance mode: leave them on, suspend or power off. Removable media mounted to VMs can be automatically disabled. In case entering maintenance mode fails, we can specify how many times to retry and how long to wait between retries. The settings can be saved as default host remediation options for future upgrades.
Finally, the Cluster remediation options enables changes at cluster level - disable DPM, disable Fault Tolerance, disable HA admission control. Powered off and suspended VMs can be migrated to other hosts in the cluster while a host enters maintenance mode. Finally you may select to enable parallel cluster remediation and to specify how many hosts to process in parallel or let Update Manager decide the number based on the cluster settings. Parallel remediation is applied only on hosts where VMs are powered off or suspended. Also, VSAN cluster allows only for one host to be in maintenance mode at a time. Hosts in VSAN cluster will be updated sequentially.
If remediation is sequential and one of the host fails to enter maintenance mode, Update Manager will report an error and stop the remediation process. When parallel processing is selected, if Update Manager encounters an error, it ignores the host and it continues with the next host in the cluster.
On the summary page you can run a a pre-check remediation report which will provide information about issues with the environment and will suggest what changes to apply:
Press OK and the remediation process will start. At the end of the process, the status of overall compliance in Update Manger tab will display Compliant.